The purpose of this project is to refine a previously constructed prototype impact noise generator whose peak level, rise time, and decay can be experimentally manipulated so that the effects of these parameters on hearing loss can be studied in laboratory animals. Although initial impact noise generator demonstrated that the desired sound pressure level and waveshapes could be produced the mechanical failure rate was excessive. Nevertheless it was possible to show that the response of the cochlear microphonics and action potential differed significantly between impact and continous noise of equal energy, the mechanical failure rate was excessive. A pneumatic or hydraulic driving systems was deemed necessary to withstand the hundreds of thousands of impacts necessary in a chronic exposure experiment. Arrangements are being made for the design and fabrication of a pneumatic driver.